Xanthine derivatives with adenosine-antagonistic activity

ABSTRACT

Xanthines of the formula I ##STR1## wherein R 1  is a C 1  -C 4  alkyl group: 
     R 2  is a C 1  -C 4  alkyl group; 
     R 3  tetrahydropyran-4-yl or 1,3-dithiolan or; 
     R 3  represents one of the groups of formula ##STR2## and pharmaceutically acceptable acid addition salts thereof. These are adenosine antagonists, capable of acting as cholinomimetics, useful for the treatment of CNS disorders such as senile dementia and Alzheimer&#39;s disease.

This is a continuation, of application Ser. No. 942,871, filed Sep. 10, 1992, now abandoned which is a division of application Ser. No. 691,193, filed Apr. 25, 1991, now U.S. Pat. No. 5,175,291, which is a continuation of application Ser. No. 452,643, filed Dec. 18, 1989, now abandoned.

The invention relates to new xanthine derivatives, processes for preparing them and their use as pharmaceutical compositions.

The new xanthines have the structure of general formula I ##STR3## wherein R₁ is a C₁₋₆, preferably C₁₋₄ alkyl group, a C₃ or C₄ alkenyl group or a C₃ or C₄ alkynyl group;

R₂ is a C₄ or CA alkenyl group, a C₁₋₆, preferably C₁₋₄ alkyl group, an optionally substituted benzyl group or a C₃ or C₄ alkynyl group;

R₃ represents a C-linked saturated or unsaturated five, six or seven-membered heterocyclic ring which contains one or more heteroatoms selected from the group comprising oxygen and sulphur and may optionally carry one of the following groups:

C₁₋₆, preferably C₁₋₄ alkyl, ═O, --CHO, --CH₂ OR₄, --CH₂ OR₇, COOR₄, CONR₅ R₆, whilst a furan or thiophene group may also contain one of the groups

--CH═CH--CONR₅ R₆,

--CH═C (COOR₄)₂ (R₄ being identical or different),

--CH═C (COOR₄) (CONR₅ R₆,

--CH═C (COOR₄) (CH₂ OR₄) (R₄ being identical or different),

--CH═C (COOR₄) (CH₂ OR₇),

--CH═C (CH₂ OR₄)₂,

--CH═C (CH₂ OR₇)₂, --CH═C (CONR₅ R₆) CH₂ OR₄, --CH═C (CONR₅ R₆)CH₂ OR₇ or nitro and the tetrahydrofuran group may also carry a group --(CH₂)₂ --CONR₅ R₆ ;

R₃ represents a C₄₋₈ cycloalkene which may be substituted by C₂₋₄ alkenyl,

R₃ represents a C₄₋₈, preferably C₅ and C₆, cycloalkanone or a C₄ to C₈, preferably C₅ and C₆ cycloalkanol, which may be substituted in the α-position by C₂₋₆, preferably C₂₋₄, alkenyl, C₂₋₆, preferably C₂₋₄ alkynyl, optionally substituted benzyl, CH₂ OR₄, CH₂ COOR₇ or (CH₂)₂ CN,

R₃ represents a C₃ to C₈, preferably C₅ or C₆ cycloalkane, which may optionally be substituted by C₁₋₆, preferably C₁₋₄ alkyl, ═CH₂, ═N--NH-aryl, preferably ═N-NH-phenyl, wherein the aryl or phenyl group may be substituted, ═N--NH-C₁ to C₆ alkyl, ═NOH, --OCONH-aryl, preferably --OCONH-phenyl, wherein the aryl or phenyl group may be substituted,

OCONH--C₁₋₆ alkyl, --OR₄, --OR₇, --(CH₂)₁ --COOR₄, --(CH₂)₁ --NR₄ R₄ (R₄ being identical or different), --(CH₂)₁ --CONR₅ R₆, --(CH₂)₁ --OR₄, --(CH₂)₁ --OR₇, wherein 1 represents one of the numbers 0, 1, 2, 3 or 4, or a group ═CAH wherein A represents COOR₄, CN, CONR₅ R₆, CH═CH--COOR₄, CH═CH--CONR₅ R₆, CH₂ OR₄ or CH₂ OR₇,

or the cycloalkane is substituted by C₁₋₆, preferably C₁₋₄ alkyl, vinyl, allyl, optionally substituted phenyl, optionally substituted C₁₋₄ alkylphenyl, and has as a second substituent a hydroxyl group in a geminal position relative to the first substituent;

R₃ forms together with the cycloalkane a ketal of general formula ##STR4## wherein Ra represents C₁₋₄ alkyl and

Rb represents C₁₋₄ alkyl or Ra and Rb together form a C₂₋₃ alkylene group which may optionally be mono-or disubstituted by C₁₋₅ alkyl, C₁₋₅ alkyloxycarbonyl, hydroxy C₁₋₅ alkyl, preferably hydroxymethyl;

R₃ represents an optionally substituted group of the formula ##STR5## R₃ represents a group of formula ##STR6## R₄ represents hydrogen, a C₁₋₁₃, preferably C₁₋₆ and C₁₁₋₁₃ alkyl group, an optionally substituted C₃₋₆ cycloalkyl group, an optionally substituted benzyl group, a C₃₋₁₃, preferably C₃₋₆ alkenyl, a propargyl group, a trityl group,

R₅ represents hydrogen, a C₁₋₆ preferably C₁₋₄ alkyl group, an optionally substituted C₃₋₆ cycloalkyl group;

R₆ represents hydrogen, a C₁₋₆, preferably C₁₋₄ alkyl group, an optionally substituted benzyl group, a group of general formula --(CH₂)_(n) --NR₅ R₅, --((CH₂)_(n) --O--(CH₂)_(m) --O)_(k) --(CH₂)_(n) --NR₅ R₅) (wherein R₅ is identical or different)

wherein n=2, 3, 4, 5, 6, 7 or 8, m=2, 3, 4, 5 or 6 and k=0 or 1, ##STR7## (wherein R₅ is identical or different), whilst the piperazine ring may be substituted by C₁₋₄ alkyl, preferably methyl, a C-linked piperidinyl group which is optionally substituted by C₁₋₄ alkyl or an N-linked benzyl group or

R₅ and R₆ together with the nitrogen atom form an optionally C₁₋₄ -alkyl-substituted five or six or seven-membered ring which may contain a further heteroatom selected from the group comprising oxygen, sulphur and nitrogen, whilst the nitrogen atom may be substituted by the group R₄ ;

R₇ represents an amino acid group, linked via the carbonyl function, of a naturally occurring amino acid, CO--C₁ -C₁₃ -alkyl, preferably CO--C₂ -C₄ -alkyl menthoxyacetyl, a camphanic acid group linked via a carbonyl group, abietinoyl, 4-aminobutyroyl, optionally substituted benzoyl, preferably trimethoxybenzoyl, a group of general formula CO-B, wherein B is an optionally substituted C-linked, 5, 6 or 7 membered heterocyclic group, and optionally the racemates, optically active compounds and pharmacologically acceptable acid addition salts thereof.

Preferred compounds of general formula I are those wherein

R₁ represents an unbranched C₃₋₄ alkyl group, an allyl or a propargyl group;

R₂ represents an allyl group, a C₃₋₄ alkyl group or a propargyl group;

R₃ represents a group selected from among furan, tetrahydrofuran, tetrahydrofuranone, thiophene, dithiol, dithian or tetrahydropyran which may carry one of the following substituents: methyl, ethyl, propyl, butyl, CHO, CH₂ OR₄, CH₂ OR₇, COOR₄, CONR₅ R₆,

R₃ represents a furan substituted by --CH═CH--CONR₅ R₆, --CH═C(COOR₄)₂ (R₄ being identical or different),

--CH═C (COOR₄) (CONR₅ R₆),

--CH═C (COOR₄) (CH₂ OR₄) (R₄ being identical or different),

--CH═C (COOR₄) (CH₂ OR₇),

--(CH₂)_(n) --CONR₅ R₆,

--CH═C (CH₂ OR₄)₂,

--CH═C (CH₂ OR₇)₂,

--CH═C (CONR₅ R₆)CH₂ OR₄ or

--CH═C (CONR₅ R₆) CH₂ OR₇ ;

R₃ represents a cyclopentanyl or cyclohexanyl group, optionally substituted by methyl, ethyl, propyl, isopropyl, tert-butyl, allyl, vinyl, phenyl or benzyl, whilst a hydroxy group may be present as a geminal substituent;

R₃ represents a cyclopentanyl or cyclohexanyl group, substituted by hydroxy, methoxy, ethoxy, propyloxy, trimethoxycarbonyl, isopropyloxy, optionally substituted benzyloxy, allyloxy, propargyloxy,

--CH₂ --CH₂ --OH,

--CH₂ --COOCH₃, ═CH--COOCH₃, ═C--CN,

--(CH₂)₂ NH₂

═CH₂, ##STR8## ═NOH, --CH₂ OH, OR₄ wherein R₄ ═ methyl or trityl, OR₇ wherein R₇ represents COCH₃, COC₂ H₅, COC₃ H₇, CO tert-butyl, -CO-phenyl or COCH₂ -phenyl, optionally substituted, CO-pyridyl,

--CO--(N-methyl-4H-pyridyl),

--CO--(methylpyridyl), --COCH₂ --CH═CH₂,

--CO CH₂ --C═CH;

R₃ represents a group ##STR9## wherein R_(a), R_(b) =CH₃, C₂ H₅ or R_(a) and R₆ together represent --CH₂ --CH₂ --,

R₃ represents a cyclopentanone or cyclohexanone,

R₃ represents a cycloalkane or cycloalkene with 4-8 carbon atoms, which may optionally be substituted by a straight-chained or branched C₂₋₄ alkenyl group; a cyclopentanone or cyclopentanol or cyclohexanone or cyclohexanol which may be substituted in α-position with respect to the keto or hydroxy group by C₂₋₄ alkenyl, C₃ or C₄ alkynyl, benzyl, --CH₂ CH₂ CN, (CH₂)3NR₅ R₅ (wherein R₅ is the same or different), CH₂ COOR₄, or CH₂ OR₄, wherein R₄ may represent hydrogen, methyl, ethyl or propyl;

R₃ represents norbornane or norbornene, optionally substituted, ##STR10## R₄ represents hydrogen, a C₁₋₃ alkyl, a cyclopropyl group, a cyclopentyl group, benzyl, an aryl group, a propargyl group or a triphenylmethyl group;

R₅ represents hydrogen, a C₁₋₃ alkyl group; a cyclopropyl group or a benzyl group;

R₆ represents hydrogen, methyl, ethyl, propyl,

--(CH₂)_(n) --NH₂ (n=2-8),

--(CH₂)_(n) NEt₂ (n=2,3) or

--(CH₂)₃ --O--(CH₂), --O--(CH₂)₃ --NH₂,

N-benzyl-piperidin-4-yl, or R₅ and R₆ together with the nitrogen atom represent a piperidine, piperazine or morpholine group which may optionally be substituted by a C₁₋₄ alkyl group, preferably methyl;

R₇ represents prolinoyl, CO--(CH₂)₀₋₃ --CH₃, (-)-menthoxyacetyl, a camphanic acid group linked via a carbonyl group, abietinoyl, benzoyl, 4-aminobutyroyl, 3,4,5-trihydroxybenzoyl, 3,4,5-trimethoxybenzoyl, a nicotinic acid, isonicotinic acid or picolinic acid group, an N-methylnicotinic acid group or an N-methyl-4H-nicotinic acid group, and optionally the acid addition salts thereof.

Particularly preferred compounds are the compounds of general formula I wherein R₃ forms an optionally substituted cyclopentane group in which the substituent is in the 3-position of the cyclopentane ring. It is particularly preferred for the group R₃ to represent 3-oxocyclopentane.

Examples of alkyl groups, including those which are constituents of other substituents, include methyl, ethyl, propyl, isopropyl, butyl, sec.-butyl, isobutyl, tert.-butyl, pentyl, isopentyl, neopentyl, hexyl, isohexyl and examples of longer-chained alkyl groups include decanyl, undecanyl, dodecanyl and tridecanyl and the isomers thereof. Examples of alkenyl groups include allyl (provided that it does not form any enamines), propenyl, isopropenyl, butenyl and isobutenyl. (Et=ethyl).

Examples of cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl which may be substituted by C₁₋₄ alkyl. A benzyl group, like a phenyl group, may be mono or polysubstituted by C₁₋₄ alkyl, preferably methyl, or by C₁₋₄ alkoxy, preferably methoxy, or by hydroxy and/or halogen such as fluorine, chlorine or bromine.

The term "aryl" indicates an aromatic ring system with 6 to 12 carbon atoms which may optionally be substituted by C₁₋₄ alkyl, halogen, hydroxy, nitro, C₁₋₄ alkoxy, amino, C₁₋₄ alkylamino and/or C₁₋₄ dialkylamino; the preferred aryl group is phenyl.

Examples include: 2-chlorophenyl,2-bromophenyl, 3-fluorophenyl, 2,3-dichlorophenyl, 4-hydroxyphenyl,2-methylphenyl, 4-methylphenyl, 3-ethylphenyl, 4-propylphenyl, 4-isopropylphenyl, 4-butylphenyl, 4-tert.-butylphenyl, 4-pentylphenyl, 2,4-dimethylphenyl,2-trifluoromethylphenyl, 3-trifluoromethylphenyl,2-methoxyphenyl, 4-methoxyphenyl, 3-ethoxyphenyl,₂ -propoxyphenyl, 4-butoxyphenyl, 2,4-dimethoxyphenyl, 3,4,5-trimethoxyphenyl, 2,4-dinitrophenyl, 4-nitrophenyl.

Examples of cyclic groups of general formula NR₅ R₆ include: pyrrol, pyrroline, pyrrolidine, 2-methylpyrrolidine, 3-methylpyrrolidine, piperidine--optionally mono- or polysubstituted by C₁₋₄ alkyl, piperazine, N-methylpiperazine, N-ethylpiperazine, N-n-propylpiperazine, N-benzylpiperazine, morpholine, thiomorpholine, imidazole, imidazoline, imidazolidine, pyrazole, pyrazoline, pyrazolidine in which the above-mentioned heterocyclic group may also be substituted by C₁₋₄ alkyl, preferably methyl.

Examples of heterocyclic groups which may be linked via a carbon atom include thiophene,2-methylthiophene, 2-nitrothiophene, furan,2-nitrofuran, tetrahydrofuran, 2-methyltetrahydrofuran,2-hydroxymethylfuran, tetrahydrofuranone, γ-butyrolactone, α-pyran, γ-pyran, 1,3-dioxolan, 1,2-oxathiolan, 1,2-oxathiepan, tetrahydro-pyran, thiolan, 1,3-dithian, 1,3-dithiolan, 1,3-dithiolene and furfural, in which the heterocyclic group may be substituted as specified in the definitions.

Examples of heterocyclic groups which may be linked via a carbon atom and contain at least one nitrogen atom include: pyridine, pyrrol, pyrroline, pyrrolidine, piperidine, piperazine, morpholine, thiomorpholine, imidazole, imidazoline, imidazolidine, pyrazole, pyrazoline, pyrazolidine, in which the above-mentioned heterocyclic groups may be substituted by C₁₋₄ alkyl.

Examples of naturally occurring amino acids include alanine, valine, leucine, isoleucine, proline, phenylalanine, tryptophane, methionine, glycine, serine, threonine, cysteine, tyrosine, asparagine, glutamine, histidine, arginine, lysine.

The compounds according to the invention are adenosine antagonists; in particular they have a high affinity (up to 1.6 nM) for the A₁ -receptor and a high selectivity for this receptor subtype.

In hippocampal slices the substances antagonise the adenosine-induced suppression of the population spikes after electrical stimulation. In vivo, an increased acetylcholine content can be detected in the rat's brain.

These results indicate that the xanthine derivatives described intensify the natural cell activity of cholinergic neurones in the brain and thus prove to be functional cholinomimetics with a central attack. EEG investigations on cats indicate a significant increase in vigilance.

Substances of this kind are of great interest for the symptomatic treatment of degenerative diseases of ageing such as senile dementia and Alzheimer's disease.

The high receptor affinity should make it possible to use low doses for treatment so that there are virtually no side effects which cannot be put down to the blocking of adenosine receptors. Similarly, because of the high A₁ selectivity of the compounds, A₂ -dependent side effects should not occur. In addition to being used as geronto-psychoactive drugs and nootropics, the adenosine antagonists described could also be used to treat cardiac and circulatory disorders.

Other possible indications are degenerative diseases such as organic brain syndrome, Parkinson's disease, traumatic CNS damage, post/neurological deficit, respiratory depression (intoxication, post op) and neonatal brain damage.

Pharmacological results are shown in Table Ia. The test methods correspond to those recited in the following literary references:

Lohse M. J., V. Lenschow and U. Schwabe (1984) Mol. Pharmacol 26, 1-9; Virus, M. R., T. Baglajewski and M. Rachelovacki (1984) Neurotiology of Agenig 5, 61-62;

Daly, J. W., W. Padgett, M. T. Shamin, P. Butts-Lamb and J. Waters (1985) J. Med. Chem. 28, 487-492;

Bruns, R. F., G. H. Lu and T. A. Pugsley (1986) Mol. Pharmacol. 29, 331-346

                  TABLE Ia                                                         ______________________________________                                         Examples according to                                                                            K.sub.i [nMol]                                               Table I           (A.sub.1)                                                    ______________________________________                                         22                8 · 10.sup.-9                                       24                3 · 10.sup.-9                                       28                6 · 10.sup.-9                                       33                3 · 10.sup.-9                                       39                4 · 10.sup.-9                                       40                2 · 10.sup.-9                                       45                2 · 19.sup.-9                                       49                2 · 10.sup.-9                                       50                2 · 10.sup.-9                                       ______________________________________                                    

The compounds according to the invention may be prepared by analogous methods known per se.

In general, 8-substituted 1,3-dialkylxanthines are obtained by reacting 1,3-dialkyldiaminouracils with aldehydes, carboxylic acids or carboxylic acid chlorides or by reacting 1,3-dialkyl-6-amino-5-nitrosouracils with aldehydes.

5,6-Diamino-1,3-dimethyluracil is commercially obtainable; derivatives substituted with other groups are prepared by reacting the corresponding dialkylurea with cyanoacetic acid with subsequent nitrosation and optional hydrogenation or reduction with dithionite to obtain the diamine (J. Org. Chem. 16, 1879 (1951) and Can. J. Chem. 46, 3413 (1968)). ##STR11##

Xanthines with a benzyl group in the 3-position and a different group in the 1-position are obtained by 1-alkylation of corresponding precursor molecules which are substituted in the 3-position with a benzyl group and in the 8-position accordingly.

These can be obtained by reacting monobenzylurea and cyanoacetic acid to produce 6-amino-1-benzyluracil (L.-F. Tietze and Th. Eicher, Reaktionen und Synthesen, Georg Thieme Verlag, Stuttgart 1981, p. 322), alkylation with the desired group in the 3-position (XIV), nitrosation of the 5-position (XV) and hydrogenation to yield the 3-substituted 1-benzyl-5,6-diaminouracil (XVI). Aldehydes, carboxylic acids and acid chlorides used for the reaction with 5,6-diaminouracils can be prepared by methods known from the literature.

In suitable cases, the xanthines described may be produced by reacting 1,3-dialkyl-6-chlorobarbituric acids with H₂ N-CH₂ -R₃, followed by nitrosation and cyclisation (see J. Med. Chem. 32, 1231 (1989). ##STR12##

Using the processes thus described, it is possible to prepare xanthine derivatives in which R₃ has the following meaning, for example:

Thiophene,2-methylthiophene,2-nitrothiophene, furan, cyclohexan, cyclohexanone, tetrahydrofuranone, 1,3-dithiane, pyran, cyclobutane, cyclohexan, norbornene and others, provided that the corresponding aldehydes R₃ CHO, carboxylic acids R₃ COOH or reactive derivatives thereof, already functionalised, can be reacted with the corresponding diaminouracil.

Other synthetic variations can then be effected on the "basic xanthine structures" thus obtained.

If desired, reactive functional groups can be protected in the usual way. Starting from the corresponding 8-cycloalkanones, the corresponding alcohols may be prepared by reduction and can then in turn by esterified with carboxylic acids or acid chlorides or reacted with isocyanates to form carbamates. By reacting the corresponding ketones with hydroxylamines the corresponding oximes may be obtained, or, with substituted hydrazines, the corresponding hydrazones. The ketone function can be ketalised with alcohols in the usual way. Reduction of the ketals-- for example using LiAlH₄ /AlCl₃ --yields the corresponding ethers. (In all the formulae which follow the positions of the groups are given solely by way of example without restricting the compounds according to the invention to the positions specified). ##STR13## n=1-5; X= "xanthine"

Wittig-Horner reactions on the ketone functions with phosphonic acid esters result in substituted olefins. By esterification of the carboxyl groups, amide formation and reduction to yield the alcohol with subsequent esterification or etherification, substituted compounds of the type specified below can be obtained, and these can subsequently be subjected to hydrogenation. ##STR14##

8-Furyl or 8-thiophenyl derivatives may be formylated according to Vilsmeier (IV). The aldehydes thus obtained are used as starting materials for Wittig-Horner reactions (X) with phosphonates; the products can be further derivatised in accordance with the methods specified above. ##STR15## A=O, S; Z=extracting group, X=xanthine

The aldehydes are suitable for Knoevenagel reactions (XI) with malonic esters. The ester groups may be reduced to form alcohols and these may be esterified or etherified. Saponification of one of the ester groups yields the monocarboxylic acid. This serves as a starting material for the synthesis of "mixed-functional" derivatives. Thus, the combinations of ester (amide, alcohol (including esterified or etherified)/carboxylic acid, alcohol (including esterified or etherified)/amide, alcohol (including esterified or etherified)/ester, mixed ester may be obtained. ##STR16## x=xanthine A=O, S;

By reduction, the corresponding alcohols, which may be esterified and etherified, are obtainable from the aldehydes.

Reactions of oxidation yield carboxylic acids which may in turn be converted into the esters and amides. ##STR17##

The double bond in 8-norbornenyl derivatives may be converted by reaction with KMnO₄ to yield the cis-diol. Reaction with m-chloroperbenzoic acid yields the epoxide which can be opened to yield the trans-diol, reacted with sodium azide to form the azido alcohol or reduced with lithium tetrahydridoalanate to yield the corresponding alcohol. The α-amino alcohol can be obtained by hydrogenation.

Starting from xanthine derivatives wherein R₃ represents a cycloalkanone, derivatives of general formula ##STR18## wherein R₈ represents methyl, ethyl, butyl, tert.-butyl, vinyl, phenyl and benzyl, are obtained by Grignard reaction or by reacting with Li-organic reagents.

The above-mentioned cycloalkanones may be converted with the so-called Nozaki-Lombardo reagent into the corresponding methylene derivatives which can subsequently be reduced to yield the methyl compounds (J. Org. Chem. 50 (8), 1212 (1985) or after hydroboration with BH₃ --CH₃ SCH₃ /H₂ O₂, OH⁻ yield the hydroxymethyl derivatives.

Reduction of the carbonyl group in optionally substituted cycloalkanones, e.g. using sodium tetrahydridoboranate, produces the corresponding alcohols which can be esterified or etherified in the subsequent reaction steps. Enantiomerically pure xanthine derivatives which carry a cyclopentane group as the substituent R₃ may be prepared according to the following plan: ##STR19##

The general procedures XVIII and XIX contain other details of stereospecific synthesis.

1,3-Dipropyl-8-[3-hydroxycyclopentyl]xanthine is esterified enantioselectively with lipases in organic solvents. By subsequent purification of the residual alcohol, according to the same process the (-)-rotatary enantiomer is obtained with a purity of more than 99.5%.

Reductive cleavage of the acetate first obtained using lithium aluminium hydride yields the optically enriched (+)-alcohol, which is obtained with an enantiomeric purity of more than 99.9% by reacting with a second lipase. From these optically pure substances a whole range of optically active xanthine derivatives can be obtained with substituted cyclopentane groups in the 8-position using the methods specified.

Suitable compounds according to the invention may be converted into the acid addition salts thereof using methods known per se.

Acids suitable for salt formation include for example hydrochloric, hydrobromic, hydriodic, hydrofluoric, sulphuric, phosphoric, acetic, propionic, butyric, caproic, valeric, oxalic, malonic, succinic, maleic, fumaric, lactic, tartaric, citric, malic, benzoic, p-hydroxybenzoic, p-aminobenzoic, phthalic, cinnamic, salicylic, ascorbic and methanesulphonic acid, 8-chlorotheophylline and the like.

The preferred acid addition salts are the hydrochlorides and hydrobromides.

General procedure I: cyclisation with aldehyde

EXAMPLE 1

1,3-Dipropyl-8-(1,4-benzodioxan-6-yl)xanthine

2.18 g (0.013 mol) of 1,4-benzodioxan-6-aldehyde, 80 ml of ethanol and 2.4 ml of glacial acetic acid are mixed together and 2.8 g (0.012 mol) of 5,6-diamino-1,3-diprpyluracil are added thereto. The clear solution is refluxed for 21/4 hours and then cooled to 60° C. At this temperature, 2.1 ml (0.013 mol) of diethylazodicarboxylate are added dropwise and the viscous suspension produced is mixed with 80 ml of ethanol and refluxed for 2 hours. After a further 20 hours at ambient temperature the mixture is cooled to 5° C., the solid matter is filtered under suction and washed with ethanol and ether. 4.1 g of the title compound are obtained in the form of a grey solid (=92% of theory), melting point 280°-282° C.

General procedure Ia: cyclisation with aldehydes

EXAMPLE 1a

1-Propyl-3-benzyl-8-(1,4benzodioxan-6-yl)xanthine

2.9 g (0.01 mol) of 1-benzyl-3-propyl-5-nitroso-6-aminouracil are added to 60 ml of dimethylformamide together with 2.3 g (0.014 mol) of 1,4-benzodioxan-6-aldehyde, then 0.5 g (0.014 mol) of 1,1-dimethylhydrazine are added and the mixture is refluxed for 8 hours. After working up in the usual way, the crystalline residue is triturated with ethanol and filtered under suction. 1.0 g of the title compound is obtained in the form of yellow crystals, m.p. 290° C.

General procedure II: cyclisation with carboxylic acid

EXAMPLE 2

1,3-Dipropyl-8-(tetrahydropyran-4-yl)xanthine

3.2 g (0.025 mol) of tetrahydropyran-4-carboxylic acid, 4.0 g (0.025 mol) of carbonyldiimidazole and 85 ml of absolute methylene chloride are stirred for 30 minutes at ambient temperature. After the addition of 5.7 g (0.025 mol) of 5,6-diamino-1,3-dipropyluracil, the mixture is stirred for 4 hours at ambient temperature and then evaporated down in vacuo. The residue is combined with 130 ml of water and 11.6 g of calcium hydroxide, stirred for 30 minutes at 80° C. and, after cooling, acidified with conc. HCl whilst cooling with ice. The mixture is extracted with ethyl acetate and the organic phase is dried and evaporated. Chromatography of the crystalline residue on silica gel (CH₂ Cl₂ CH₃ OH 99:1) yields 1.7 g of the title compound in the form of white crystals (15% of theory), m.p. 171°-172° C.

EXAMPLE 2a

1,3-Dipropyl-8-(3-oxocyclopentyl)-xanthine

2.4 g (0.014 mol) of 1,4-dioxaspiro[4,4]nonan-7-carboxylic acid are dissolved in 56 ml of methylene chloride and after the addition of 2.2 g (0.014 mol) of carbonyldiimidazole stirred for 1 hour at ambient temperature. Then 3.2 g (0.014 mol) of 5,6-diamino-1,3dipropyluracil are added and the mixture is stirred for a further 4 hours at ambient temperature. The solution is evaporated down in vacuo, the oily residue is mixed with 70 ml of water and 4.5 g of Ca(OH)₂ and stirred for 1 hour at 70° C. 100 ml of 50% NaOH are added, the mixture is stirred for a further hour at 70° C. and for 16 hours at ambient temperature. Whilst being cooled with ice, the solution is adjusted to pH 6 with HCl and extracted with methylene chloride. After drying and evaporation in vacuo the combined organic phases yield a crystalline residue which is recrystallised from ethanol using activated charcoal. 0.8 g (16%) of white crystals are obtained, m.p. 147°-148° C.

The dioxolan protecting group is then hydrolysed with acid in the manner known from the literature and the title compound is obtained.

EXAMPLE 2b

1,3-Dipropyl-8-(3-oxocyclopentyl)-xanthine

a) Preparation of 3-oxo-cyclopentane carboxylic acid

100.0 g of Methyl-3-oxocyclopentane carboxylate (0.7 mol) are mixed with 1000 ml of 2-molar hydrochloric acid and stirred for 10 hours at boiling temperature. The solution is cooled and fully concentrated by evaporation in vacuo. The residual water is drawn off 3 times with 50 ml of toluene each time (toluene is added to the residue and distilled off using a Rotavapor under a full water-jet vacuum and at a water bath temperature of 60°-70° C). The crude yield is fractionally distilled in a high vacuum.

1st fraction: Bp₀.02 20°-110° C. (yield: 1.2 g of oil)

2nd fraction: Bp₀.02 110°-116°

yield: 4.7 g of partly crystalline oil

3rd fraction: Bp₀.02 116°-121° C.

yield: 74.0 g of colourless oil which later crystallised out.

Yield 74.0 g (82.1% of theory)

8.8 g of 3-oxocyclopentane carboxylic acid (0.072 mol) are placed in 240 ml of absolute methylene chloride and at 20°-25° C., with stirring, 11.6 g of carbonyldiimidazole are added and the resulting mixture is stirred for 2 hours at ambient temperature. The reaction mixture is evaporated to dryness in vacuo. The oily residue is mixed with 3200 ml of distilled water and 35 g of calcium hydroxide and stirred at 80° C. for 0.5 hours. It is then cooled to 5° C. and adjusted to pH 1-2 using conc. hydrochloric acid and extracted 3 times, each time with 100 ml of CH₂ Cl₂. The combined organic phases are washed once with 100 ml of water, dried with magnesium sulphate, filtered and evaporated to dryness. The crude yield is purified over 350 g of silica gel S160 using about 41 of eluant CH₂ Cl₂ :CH₃ OH 99:1. The clean fractions are evaporated to dryness. The crystalline residue is triturated with 100 ml of ether and filtered under suction.

Yield: 11.5 g of grey crystals (50.2% of theory) M.p.: 164°-168° C.

General procedure III: cyclisation with acid chloride

EXAMPLE 3

1,3-Dipropyl-8-(4,7,7-trimethyl-2oxo-bicyclo[2.2.1]-heptan-3-on-1-yl)xanthine

1.2 g (5.4 mmol) of 5,6-diamino-1,3-dipropyluracil and 1.0 g of triethylamine (10 mmol) are dissolved in 50 ml of absolute methylene chloride. After the dropwise addition of 1.2 g (5.5 mmol) of camphanyl chloride, the mixture is stirred for 20 hours at ambient temperature and concentrated by evaporation in vacuo. The residue is mixed with 28 ml of water and 1.7 g of calcium hydroxide and stirred for 3 hours at 80° C. The cooled suspension is acidified whilst being cooled with ice and then extracted with methylene chloride. The combined organic phases are dried and evaporated down and the residue is purified by chromatography on silica gel (CH₂ Cl₂ CH₃ OH 99:1).

200 mg of the title compound are obtained in the form of white crystals (10% of theory), m.p. 200°-201° C.

General procedure IV: Vilsmeier reaction

EXAMPLE 4

1,3-Dipropyl-8-(2-formylfurnan-5-yl)xanthine

At 0°-10° C. 16.4 g (0.11 mol) of phosphorus oxychloride are added dropwise to 400 ml of absolute dimethylformamide. At 5°-15° C. a solution of 15.0 g (0.05 mol) of 1,3-dipropyl-8-furanylxanthine in 330 ml of dimethylformamide is added thereto. The mixture is stirred for 1 hour at ambient temperature and for 7 hours at 85° C. The mixture is poured onto 500 ml of ice and extracted with methylene chloride. The combined organic extracts are dried and evaporated down in vacuo and the residue is crystallised from ether. 12.1 g of the title compound are obtained in the form of brown crystals (73% of theory), m.p. 215°-217° C.

General procedure V: oxidation of an aldehyde to form the acid

EXAMPLE 5

1,3-Dipropyl-8-(2-carboxyfuran-5-yl)xanthine

A solution of 0.26 g (1.5 mmol) of silver nitrate in 2 ml of water is shaken with a solution of 0.4 g of sodium hydroxide in 1 ml of water for 5 minutes. The grey-black silver oxide precipitate is filtered under suction and washed with water, then taken up in 5 ml of water and mixed with 1,3-dipropyl-8-[5-formyl-(2-furanyl)]xanthine. The mixture is heated to 50° C. and a solution of 0.1 g of sodium hydroxide in 2 ml of water is slowly added dropwise. The resulting mixture is stirred for 15 minutes at 50° C. and for 1 hour at ambient temperature and then filtered. The filtrate is acidified and mixed with methylene chloride, the precipitate formed is filtered under suction and washed with methylene chloride and ether. 0.4 g of the title compound are obtained in the form of light brown crystals (77% of theory).

General procedure VI: Knoevenagel reaction

EXAMPLE 6

1,3-Dipropyl-8-[2-(2,2-bis(ethoxycarbonyl)vinyl)-furan-5-yl]xanthine

2.5 g (7.6 mmol) of 1,3-propyl-dipropyl-8-[5-formyl-(2-furanyl)]xanthine, 1.2 g (7.6 mmol) of diethylmalonate, 0.03 g (0.3 mmol) of piperidine, 0.09 g (1.5 mmol) of glacial acetic acid and 5 ml of benzene p.a. are combined and boiled for 6 hours using a water separator. After the mixture has cooled it is diluted with 10 ml of toluene, the solid matter is suction filtered and dissolved in 100 ml of warm methylene chloride. The solution is filtered, the filtrate is evaporated down in vacuo and the residue is recrystallised from propan-2-ol. 1.0 g of the title compound are obtained in the form of yellow crystals (28% of theory), m.p. 220°-222° C.

General procedure VII: general preparation of amides

EXAMPLE 7

1,3-Dipropyl-8-[2-(N,N-diethylaminocarbonyl)furan-5-yl]-xanthine

1.0 g (2.9 mmol) of 1,3-dipropyl-8-[2-carboxy-furan-5-yl)]xanthine are dissolved in absolute dimethyl formamide and at 0°-5° C. 0.38 g of triethylamine and 0.45 g (3.3 mmol) of isobutylchloroformate are added thereto. The mixture is stirred for 2 hours at 0°-5° C., then 0.34 g (2.9 mmol) of N,N-diethylamino-ethylamine are added, and the mixture is stirred for approximately a further 12 hours in a thawing ice bath. The mixture is evaporated down in a high vacuum, methylene chloride and water are added, the mixture is made alkaline and extracted with methylene chloride. The organic phases are discarded, the aqueous phase is acidified and extracted once more. The combined organic extracts are dried, filtered and evaporated down and the residue is crystallised from ethyl acetate. 0.25 g of the title compound are obtained in the form of yellowish crystals, m.p. 247°-250° C.

General procedure VIII: reduction of a ketone or aldehyde to form the alcohol

EXAMPLE 8

1,3-Dipropyl-8-(1-hydroxycyclopent-3-yl)xanthine

0.5 g (1.6 mmol) of 1,3-dipropyl-8-(1-oxo-3-cyclopentyl)xanthine, 10 ml of ethanol and 0.1 g (2.6 mmol) of sodium tetrahydridoboranate are stirred for 21/2 days at ambient temperature. The mixture is evaporated down in vacuo and mixed with water and methylene chloride then the aqueous phase is acidified and extracted. The combined organic extracts are dried and evaporated down in vacuo. The residue is separated into the isomers by chromatography on silica gel (CH₂ Cl₂ /CH₃ OH 95:5). From the 1st fraction, 0.4 g of the title compound are obtained in the form of white crystals (39% of theory), m.p. 174°-176° C. and from the 2nd fraction 0.4 g of the title compound are obtained in the form of white crystals (39% of theory), m.p. 191°-193° C.

General procedure IX: acylation of an alcohol

EXAMPLE 9

1,3-Dipropyl-8-[1-((4,7,7-trimethyl-2-oxabicyclo[2.2.1]-heptan-3-on-1-yl)carbonyloxy)cyclopentan-3-yl]xanthine

0.2 g (0.6 mmol) of 1,3-dipropyl-8-(1-hydroxy-3-cyclopentyl)xanthine and 0.24 g (3 mmol) of pyridine are mixed into 10 ml of absolute methylene chloride and after the addition of 0.2 g (0.9 mmol) of camphanyl chloride, the mixture is stirred for 4 hours at ambient temperature. Water is then added and the aqueous phase is separated off. The organic phase is dried and evaporated down in vacuo, then the residue is purified by chromatography on silica gel (CH₂ Cl₂ /CH₃ OH 95:5). 50 mg of the title compound are obtained in the form of a yellowish oil.

General procedure X: Wittig-Horner reaction

EXAMPLE 10

1,3-Dipropyl-8-(1-cyanomethylenecyclopent-3-yl)xanthine

0.28 g (1.6 mmol) of diethylcyanomethane phosphonate are dissolved in 20 ml of absolute benzene and refluxed for 5 hours with 0.13 g (3.2 mmol) of a 60% sodium hydride dispersion. The mixture is evaporated down in vacuo and taken up in methylene chloride and water and then acidified. The aqueous phase is extracted and the combined organic extracts are dried and evaporated down. Subsequent chromatography of the residue on silica gel (CH₂ Cl₂ /CH₃ OH 97:3) yields 0.1 g of the title compound in the form of a colourless oil (18% of theory).

General procedure XI: hydrogenation of double bonds

EXAMPLE 11

1,3-Dipropyl-8-(norbornan-2-yl)xanthine

1.0 g (3.1 mmol) of 1,3-dipropyl-8-(5-norbornen-2-yl)xanthine are hydrogenated under pressure in 30 ml of ethanol, with the addition of palladium/charcoal, until no further uptake of hydrogen can be detected. The catalyst is filtered off, the filtrate is concentrated by evaporation and the residue is chromatographed on silica gel (Ch₂ Cl_(2/) CH₃ OH 99:1). 0.4 g of the title compound are obtained in the form of white crystals (39% of theory), m.p. 136°-138° C.

General procedure XII: saponification of an ester

EXAMPLE 12

1,3-Dipropyl-8- (2- (2'-ethoxycarbonyl-2'-carboxyvinyl)-furan-5-yl)xanthine

3.2 g (6.8 mmol) of 1,3-dipropyl-8-[2-(2', 2'-bis(ethoxycarbonyl)vinyl)-furan-5-yl]xanthine are added to a solution of 0.8 g (1.4 mmol) of potassium hydroxide in 20 ml of ethanol and the mixture is refluxed for 4 hours. After cooling, it is diluted with 50 ml of water and extracted with methylene chloride. The aqueous phase is acidified whilst being cooled with ice and the precipitate formed is filtered off and washed with water. 2.2 g of the title compound are obtained in the form of yellow crystals (73% of theory), m.p. 252°-253° C.

General procedure XIII: reduction of an ester to obtain the alcohol

1.7 mmol of the ester are dissolved in 5 ml of tetrahydrofuran and added dropwise to a suspension of lithium alanate (0.04 g, 1.1 mmol) in 5 ml of tetrahydrofuran. The mixture is stirred at ambient temperature for 36 hours and mixed with saturated diammonium tartrate solution. The aqueous phase is extracted with ethyl acetate, the combined organic extracts are dried and evaporated down in vacuo. The product is purified by crystallisation or by chromatography on silica gel.

General procedure XIV: N-alkylation

EXAMPLE 13

1-Benzyl-3-propyl-6-aminouracil

3.0 g (0,014 mol) of 1-benzyl-6-aminouracil are stirred for 3 hours at 70° C. with 2.2 g (0.018 mol) of n-propyl bromide, 4.2 ml of 15% sodium hydroxide solution and 7 ml of ethanol. The mixture is poured onto ice and extracted with methylene chloride. The organic phases are dried and evaporated down. The residual oil is crystallised from a mixture of methylene chloride and methanol. 1.62 g of the title compound are obtained in the form of white crystals (47% of theory), m.p. 189°-192° C.

General procedure XV: nitrosation

EXAMPLE 14

1-Benzyl-3-propyl-5-nitroso-6-aminouracil

2.0 g (7.7 mmol) of 6-amino-1-benzyl-3-propyluracil are heated to 80° C. in 15 ml of water and mixed with a solution of 0.55 g of sodium nitrite in 3 ml of water. After the addition of 1 ml of glacial acetic acid a red solid is precipitated. The pH is adjusted to 4 and the suspension is stirred for a further 30 minutes at 80° C. After cooling, the crystals are filtered under suction and washed with water. 1.9 g of the title compound are obtained in the form of reddish-violet crystals (86% of theory), m.p. 208°-212° C./decomposition.

General procedure XVI: hydrogenation of the nitroso compound

The 3-substituted 6-amino-1-benzyl-5-nitrosouracils is taken up in methanol and, after the addition of Raney nickel, hydrogenated under pressure. The catalyst is filtered off, the filtrate is evaporated down and the residue is purified by crystallisation or chromatography.

General procedure XVII: etherification

Etherification of alcohols was carried out by deprotonation of the hydroxy function using a strong base (e.g. sodium hydride in tetrahydrofuran or dimethylformamide, sodium hydroxide) and reaction with an electrophile of the type R-X, wherein X may be halogen, tosyl, mesyl or the like.

General procedure XVIII:

EXAMPLE 15

(+) -1,3 -Dipropyl-8- (3 -hydroxycyclopentyl)xanthine

a) 2.0 g (6.2 mmol) of racemic 1,3-dipropyl-8-(3-hydroxycyclopentyl)xanthine are suspended in 21 of absolute toluene and mixed with 640 mg of acetic anhydride and 2.0 g of lipase from candidacylindracea, with vigorous stirring. After 6 hours at ambient temperature the enzyme is filtered off and washed with methanol. The combined filtrates are evaporated to dryness in vacuo and the residue is chromatographed with CH₂ Cl₂ /CH₃ OH 95:5 on silica gel.

b) 0.6 g of acetylated product are obtained, which is dissolved in 22 ml of absolute THF and, after the addition of 70 mg of lithium aluminium hydride, stirred for 2 hours at ambient temperature. Whilst the mixture is cooled with ice it is hydrolysed dropwise with 5 ml of H₂ O, acidified and extracted with methylene chloride. The organic phase is dried and evaporated down and the residue is chromatographed with CH₂ Cl_(2/) CH₃ OH 95:5 on silica gel. 490 mg of alcohol are obtained with an optical rotation [α]_(D) ²⁰ =+12. (c=0.4, methanol).

c) The optically enriched alcohol is dissolved in 490 ml of absolute methylene chloride and mixed with 490 mg of acetic anhydride and 1.5 g of lipase "Amano P". The mixture is stirred for 24 hours at ambient temperature, filtered to remove the enzyme and the filtrate is evaporated to dryness in vacuo. Chromatography on silica gel using CH₂ Cl₂ /CH₃ OH 95:5 yields 480 mg of alcohol of the title compound with an optical rotation [α]_(D) ²⁰ =+18.2 (C=0.5, CH₃ OH); optical purity according to HPLC >99%.

General procedure XIX:

EXAMPLE 16

(-) -1.3-Dipropy-8-(3-hydroxy-cycopentyl)xanthine

a) 1.0 g of racemic 1,3-dipropyl-8-(3-hydroxycyclopentyl)xanthine are suspended in 11 of absolute toluene and stirred with 320 g of acetic anhydride and 1.0 g of lipase from Candida cylindracea for 8 hours at ambient temperature. The mixture is filtered to remove the enzyme, then washed with methanol and the filtrates are evaporated to dryness in vacuo. The residue is chromatographed on silica gel using CH₂ Cl₂ CH₃ OH 95:5. 0.45 g of crystalline residue is obtained, which is then triturated with ether and filtered under suction. This yields 350 mg of crystals with an optical rotation [α]_(D) ²⁰ -13.7 (c=0.4, CH₃ OH)

b) The optically enriched alcohol is once again stirred in toluene with 110 mg of acetic anhydride and 350 mg of lipase from Candida cylindracea for 16 hours at ambient temperature. The mixture is worked up as described above. Yield: 200 mg of colourless crystals, optical rotation [α]_(D) ²⁰ =-20.2 (c=0.5, CH₃ OH), enantiomeric purity according to HPLC >99.5%.

General procedure XIX:

EXAMPLE 16

(+) and (-)-1,3,dipropyl-8-(3-oxocyclopentyl)xanthine

1.0 g of optically pure alcohol 28 is dissolved in 30 ml of absolute methylene chloride and after the addition of 1.1 g of pyridinium chlorochromate the mixture is stirred at ambient temperature for 2.5 hours. The mixture is washed twice with H₂ O, the aqueous phases are extracted with methylene chloride and the combined organic phases are dried and evaporated down in vacuo. Purification is carried out by chromatography on silica gel using CH₂ Cl₂ /CH₃ OH 99:1, 98:2 and 97:3.

Depending on the optically pure alcohol used, the following compounds are obtained.

(+) alcohol yields (-) 1,3-dipropyl-8-(3-oxocyclopentyl)xanthine [α]_(D) ²⁰ -8.3 (C=0.5, methanol);

(-)alcohol yields (+) 1,3-Dipropyl-8-(3-oxocyclopentyl)xanthine [α]_(D) ²⁰ 8.0 (c=0.5, methanol).

The official chemical abstract nomenclature of these compounds is: 8-(3-oxocyclopentyl)-1,3-dipropyl-7H-purin-2,6-dione.

The compounds listed in Table I can be prepared analogously to the procedures described or according to known analogous methods.

                                      TABLE I                                      __________________________________________________________________________                                               M.pt                                 No. R.sup.1                                                                             R.sup.2                                                                             R.sup.3                     (°C.)                         __________________________________________________________________________     1   n-C.sub.3 H.sub.7                                                                   n-C.sub.3 H.sub.7                                                                    ##STR20##                  272-274                              2   "    "                                                                                    ##STR21##                  276-277                              3   "    "                                                                                    ##STR22##                  258-259                              4   "    "                                                                                    ##STR23##                  283-284                              5   "    "                                                                                    ##STR24##                  262-263                              6   "    "                                                                                    ##STR25##                  220-222                              7   "    "                                                                                    ##STR26##                  252-253                              8   "    "                                                                                    ##STR27##                  252-253                              9   "    "                                                                                    ##STR28##                  255                                  10  "    "                                                                                    ##STR29##                  253-255                              11  n-C.sub.3 H.sub.7                                                                   n-C.sub.3 H.sub.7                                                                    ##STR30##                  247-250                              12  "    "                                                                                    ##STR31##                  210-217                              13  "    "                                                                                    ##STR32##                  235-236                              14  "    "                                                                                    ##STR33##                  280-282                              15  "    "                                                                                    ##STR34##                  291-294                              16  "    "                                                                                    ##STR35##                  >300                                 17  "    "                                                                                    ##STR36##                  228-229                              18  CH.sub.3                                                                            CH.sub.3                                                                             ##STR37##                  228-230                              19  CH.sub.3                                                                            CH.sub.3                                                                             ##STR38##                  148-150                              20  n-C.sub.3 H.sub.7                                                                   n-C.sub.3 H.sub.7                                                                    ##STR39##                  135-137                              21  "    "                                                                                    ##STR40##                  195-196                              22  "    "                                                                                    ##STR41##                  171-172                              23  CH.sub.3                                                                            CH.sub.3                                                                             ##STR42##                  275-277                              24  n-C.sub.3 H.sub.7                                                                   n-C.sub.3 H.sub.7                                                                    ##STR43##                  213-213                              25  "    "                                                                                    ##STR44##                  205-207                              26  "    "                                                                                    ##STR45##                  197-198                              27  "    "                                                                                    ##STR46##                   80-83                               28  "    "                                                                                    ##STR47##                  186-187                              29  CH.sub.3                                                                            CH.sub.3                                                                             ##STR48##                  260                                  30  n-C.sub.3 H.sub.7                                                                   n-C.sub.3 H.sub.7                                                                    ##STR49##                  179-181                              31  "    "                                                                                    ##STR50##                  197-198                              32  CH.sub.3                                                                            CH.sub.3                                                                             ##STR51##                  273-275                              33  n-C.sub.3 H.sub.7                                                                   n-C.sub.3 H.sub.7                                                                    ##STR52##                  165-167                              34  "    "                                                                                    ##STR53##                  138-140                              35  CH.sub.3                                                                            CH.sub.3                                                                             ##STR54##                  292                                  36  "    "                                                                                    ##STR55##                  210-220                              37  n-C.sub.4 H.sub.9                                                                   n-C.sub.4 H.sub.9                                                                    ##STR56##                  142-150                              38  CH.sub.3                                                                            CH.sub.3                                                                             ##STR57##                  292                                  39  n-C.sub.3 H.sub.7                                                                   n-C.sub.3 H.sub.7                                                                    ##STR58##                  174-176                              40  "    "                                                                                    ##STR59##                  191-193                              41  CH.sub.3                                                                            CH.sub.3                                                                             ##STR60##                  277-280                              42  n-C.sub.3 H.sub.7                                                                   n-C.sub.3 H.sub.7                                                                    ##STR61##                  213-216                              43  "    "                                                                                    ##STR62##                  101-112                              44  "    "                                                                                    ##STR63##                  156-157                              45  "    "                                                                                    ##STR64##                  166-168                              46  "    "                                                                                    ##STR65##                  144-148                              47  "    "                                                                                    ##STR66##                  151-152                              48  "    "                                                                                    ##STR67##                  146-147                              49  "    "                                                                                    ##STR68##                  137-139                              50  "    "                                                                                    ##STR69##                  136-138                              51  "    "                                                                                    ##STR70##                  200-201                              52  "    "                                                                                    ##STR71##                  162                                  53  "    "                                                                                    ##STR72##                  180                                  54  "    "                                                                                    ##STR73##                  164-165                              55  "    "                                                                                    ##STR74##                  134-135                              56  "    "                                                                                    ##STR75##                  148-151                              57  "    "                                                                                    ##STR76##                  128-147                              58  "    "                                                                                    ##STR77##                  199-203                              59  "    "                                                                                    ##STR78##                  167-168                              60  "    "                                                                                    ##STR79##                  155-157                              61  "    "                                                                                    ##STR80##                   83-85                               62  "    "                                                                                    ##STR81##                  202-205                              63  "    "                                                                                    ##STR82##                  130-133                              64  "    "                                                                                    ##STR83##                  124-127                              65  "    "                                                                                    ##STR84##                  210-213                              66  "    "                                                                                    ##STR85##                  256-259                              67  "    "                                                                                    ##STR86##                  170-173                              68  "    "                                                                                    ##STR87##                  185-186                              69  "    "                                                                                    ##STR88##                  181-182                              70  " "  " "                                                                                  ##STR89##                  196-198 173-175                      71  "    "                                                                                    ##STR90##                  162-164                              72  "    "                                                                                    ##STR91##                  153-154                              73  "    "                                                                                    ##STR92##                  155-156                              74  "    "                                                                                    ##STR93##                  234-236                              75  "    "                                                                                    ##STR94##                  172-173                              76  "    "                                                                                    ##STR95##                  174-175                              77  "    "                                                                                    ##STR96##                  188-189                              78  "    "                                                                                    ##STR97##                  182-183                              __________________________________________________________________________

The compounds of general formula (I) may be used either on their own or in conjunction with other active substances according to the invention, possibly in conjunction with other pharmacologically active substances. Suitable forms for administration include, for example, plain or coated tablets, capsules, suppositories, solutions, syrups, emulsions or dispersible powders. Tablets may be produced, for example, by mixing the active substance or substances with known excipients, e.g. inert diluents such as calcium carbonate, calcium phosphate or lactose, disintegrants such as corn starch or alginic acid, binders such as starch or gelatine, lubricants such as magnesium stearate or talc and/or agents for obtaining delayed release such as carboxymethylcellulose, cellulose acetate phthalate or polyvinyl acetate. The tablets may also consist of several layers.

Coated tablets may be produced accordingly by coating cores made in the same way as the tablets with the substances normally used for tablet coating, such as collidone or shellac, gum arabic, talc, titanium dioxide or sugar. In order to obtain delayed release or prevent incompatibilities, the core may also consist of several layers. Similarly, the tablet coating may consist of several layers in order to obtain delayed release, and the excipients mentioned above for the tablets may be used.

Syrups of the active substances or combinations of active substances according to the invention may additionally contain a sweetener such as saccharin, cyclamate, glycerol or sugar and a flavour-enhancing agent, e.g. a flavouring such as vanillin or orange extract.

They may also contain suspension adjutants or thickeners such as sodium carboxymethylcellulose, wetting agents, e.g. condensation products of fatty alcohols with ethylene oxide, or preservatives such as p-hydroxybenzoates.

Injection solutions are prepared in the usual way, e.g. by adding perservatives such as p-hydroxybenzoates or stabilizers such as alkali metal salts of ethylenediamine-tetraacetic acid and the resulting solutions are transferred into injection vials or ampoules.

Capsules containing one or more active substances or combinations of active substances may be prepared, for example, by mixing the active substances with inert carriers such as lactose or sorbitol and encapsulating the mixture in gelatine capsules.

Suitable suppositories may be produced, for example, by mixing the active substances or combinations of active substances envisaged therefore with conventional carriers such as neutral fats or polyethylene glycol or the derivatives thereof.

The Examples which follow illustrate the invention without restricting its scope:

Examples of pharmaceutical formulations

    ______________________________________                                         A) Tablets        per tablet                                                   ______________________________________                                         Active substance  100 mg                                                       Lactose           140 mg                                                       Corn starch       240 mg                                                       Polyvinylpyrrolidone                                                                              15 mg                                                       Magnesium stearate                                                                                5 mg                                                                          500 mg                                                       ______________________________________                                    

The finely ground active substance, lactose and some of the corn starch are mixed together. The mixture is screened, then moistened with a solution of polyvinylpyrrolidone in water, kneaded, granulated whilst wet and dried. The granulate, the remaining corn starch and the magnesium stearate are screened and mixed together. The mixture is compressed to form tablets of suitable shape and size.

    ______________________________________                                         B) Tablets           per tablet                                                ______________________________________                                         Active substance     80 mg                                                     Corn starch          190 mg                                                    Lactose              55 mg                                                     Microcrystalline cellulose                                                                          35 mg                                                     Polyvinylpyrrolidone 15 mg                                                     Sodium carboxymethyl starch                                                                         23 mg                                                     Magnesium stearate    2 mg                                                                          400 mg                                                    ______________________________________                                    

The finely ground active substance, some of the corn starch, lactose, microcrystalline cellulose and polyvinylpyrrolidone are mixed together, the mixture is screened and combined with the remaining corn starch and water to form granules which are dried and screened. The sodium carboxymethyl starch and magnesium stearate are added and thoroughly mixed and the mixture is compressed to form tablets of suitable size. 

We claim:
 1. A xanthine of the formula I ##STR98## wherein R₁ is a C₁ -C₄ alkyl group;R₂ is a C₁ -C₄ alkyl group; R₃ tetrahydropyran-4-yl or 1,3-dithiolan or; R₃ represents one of the groups of formula ##STR99## or a pharmaceutically acceptable acid addition salt thereof.
 2. A xanthine of the formula I whereinR₁ represents an unbranched C₃ alkyl group; R₂ represents an unbranched C₃ alkyl group, and R₃ represents norbornanyl or norbornenyl. 